Surface Effects Ships (SES) of the type referred to as Captured Air Cushion Vehicles utilize a pressurized air bubble to maintain the vehicle above the surface of the ground or water. In marine vessels the pressurized air is maintained beneath the vessel in a plenum chamber defined between a pair of spaced depending sidewalls with bow and stern seals extending therebetween. Problems affecting performance of such vessels include the loss of pressurized air from the plenum chamber around the seals and the effect of large drag and impact forces exerted on the seals by the waves. Although various types of seal structures have been proposed which address these problems, the increased size and speed requirements of the new generation of large SES vessels, such as those currently being developed by the Navy, have precluded application of many proposed seal designs to such vessels. For example, design parameters for large SES vessels generally require a large, lightweight and flexible seal structure having rapid response characteristics to accommodate rapid variations in the water surface at high speeds. Further, the seal structures must be durable enough to endure impact and seal weight loads imposed thereon under severe sea state conditions.
A particular example of a proposed seal structure for large SES vessels is disclosed in U.S. Pat. No. 4,137,987 granted to M. Plackett. The Plackett seal generally comprises a flexible membrane transversely secured between two spaced sidewalls and a planer seal portion of juxtaposed planer members, or planers connected to the hull. These planer members depend in front of and extend beneath the flexible membrane. The planers are designed to act as planer surfaces for riding over the surface or wave discontinuities and to isolate the impact forces generated on the planers from the vessel. This is generally accomplished by supporting the free end portions of the planers with flexible supports which permit deflections in the fore and aft as well as in the up and down directions. A biasing or equilibrium means for causing the planers to return to a predetermined equilibrium position is provided by the inflatable membrane which, upon inflation, exerts an outward pressure on the forward end portion of the planer members. However, large scale seal structures, utilizing the planers embodied in the Plackett patent, have proved to be rather heavy and due to their weight and stiffness characteristics are subject to severe slamming loads as the planers encounter the waves at high speeds. Further, the heavy weight of the long planers tends to cause the seal structure to be highly stressed under severe operating conditions, such as "snap back". Snap back of the planers occurs after the lower part of the seal is forced toward the hull by a wave which, as the wave passes the seal structure, causes a gap between the lower portion of the seal and the surface of the water. Under the influence of gravity and the cushion pressure the planers accelerate toward the water until they are restrained or "snatched" by the support straps, thus exerting severe stresses in the support straps and the planer structure. Attempts to strengthen the planers tended to reduce the flexibility of the planers, which resulted in less responsive planers that, accordingly, induced higher impact forces thereon. Additionally, the interplaner joints between the juxtaposed planers have been found to be subject to undesirable tearing and chafing damage due to the relative motion between the adjacent planers. For example, the centrally supported planers permit an undesirable transverse wobble of the planers which increases the stress and strain on the interplaner joints.